Lysosomal storage diseases (LSDs) comprise a group of over 40 inherited disorders of metabolism caused by single gene mutations affecting lysosomal hydrolases. Collectively, their incidence is 1:5000 live births. While each disease has a specific clinical phenotype, they all lead to the accumulation of partially metabolized carbohydrate or lipid substrates in Lysosomes of many cells; which causes the pathologic symptoms. In general, the severity and age of onset of the clinical syndromes are determined by the level of residual enzyme activity, implying that even modes increases, if realized early in life, might affect cure. Many of the severe forms of LSDs result in marked neurologic deterioration and mental retardation for which no successful therapy is currently available. Thus, there is a compelling need to develop new approaches for treatment of LSDs with central nervous system (CNS) involvement. A key feature for therapy of these diseases is the ability of cells from both unaffected individuals and from LSD patients, to take up secreted, extracellular Lysosomal hydrolases via receptor-mediated endocytosis and to route them to Lysosomes, where they function normally. The overall goal of this grant is to use murine models for galactosialidosis and GMI-gangliosidosis to answer the fundamental question of whether a homogeneous population of overexpressing bone marrow (BM) progenitor cells can serve as a source of corrective enzyme to treat LSDs. Dr. D~Azzo will use BM from transgenic mice, overexpressing the appropriate deficient enzyme in erythroid or macrophage/monocyte lineages, for delivery of corrective protein to systemic tissues; and the CNS, of affected animals. While erythroid cells, because of their numbers, may provide a significant source of corrective enzyme to visceral organs, they hypothesize that the primary role of macrophages will be to carry the enzyme across the blood-brain barrier into the CNS. This strategy should, in principle, overcome the technical problems associated with vector-mediated gene transfer and ectopic expression. Using this approach, they will evaluate the potential of engineered BM-derived cells: 1) to serve as sources of corrective enzymes: 2) to compare the extent of correction in different organs to determine the age of recipients at which transplantation produces any benefit; 3) to confirm the idea that precursor cells of the macrophage/monocyte lineage can cross the blood-brain barrier early in life and thereby protect the CNS; and 4) to predict the longevity of efficacious treatment. The investigators postulate that results from these studies will provide crucial information for the design of expression cassettes for future use in viral or nonviral vectors, and will have direct applicability to the treatment of LSD patients. Ultimately, this approach may have general relevance to the development of gene therapy for other diseases.